1. Field of the Invention
The present invention relates to a flow-restriction device and especially to a micromechanically produced flow-restriction device.
2. Description of Prior Art
Micromechanically produced fluid passages are known e.g. in the field of fluid dosage. A simple dosing system consists e.g. of a fluid reservoir, a pressure transducer and a fluid passage having a defined flow resistance.
In addition, micromechanically produced multisensors for flow, temperature and pressure measurements are known in the field of technology. Such systems are provided with a micro-mechanical capillary on the back of a substrate and with piezoelectric pressure sensors arranged on the front of a substrate. Such known systems are disadvantageous insofar as they are difficult to produce and, in addition, insofar as the piezoelectric pressure sensors are very expensive.
DD-A-285188 discloses a flow sensor provided with a capillary and used for continuous measurements of gas volume flows. In this known flow sensor, a differential pressure between an inlet reservoir and an outlet reservoir is caused by a pressure drop via a capillary. This differential pressure is detected by means of a membrane provided with a resistance bridge which is adapted to be unbalanced, and is then used as a measure of a gas volume stream.
In the Patent Abstracts of Japan, Sect. P, Vol. 17 (1993), No. 550 (P-1624), a flow rate detection element is described, which is provided with a small channel, a pressure detection element being arranged within the walls of said channel. The pressure detected serves to control the fluid flow rate, whereby a fine control of the transport speed of the fluid can be achieved.
The publication "Einsatz von Siliziumsensoren in Proze.beta.me.beta.-geraten zur Druckmessung--Stand und Tendenzen", Technisches Messen 59 (1992) 9, pp. 340-346, contains an explanation of piezoresistive and capacitive silicon sensors and their fields of application.
EP-A-0435237 describes an electronic microvalve consisting of a silicon substrate and a freestanding, flexible, dielectric closure plate, a space being arranged between the closure plate and the silicon substrate. The silicon substrate is provided with an inlet opening, whereas the closure plate has provided therein outlet openings in such a way that said closure plate leaves the inlet opening open in a non-excited state and closes said inlet opening in an excited state.
DE-A-3814150 also refers to a valve arrangement consisting of microstructured components. In this valve arrangement, an actuating element is adapted to be moved relative to a flow path distributor for thus opening or closing fluid paths depending the respective switching position.
U.S. Pat. No. 5,377,524 discloses a microflow measurement device which makes use of a capacitive pressure sensor. In the known pressure measurement device, an inlet opening and an outlet opening are provided in a carrier plate. The carrier plate has a structured substrate arranged thereon. Said substrate is structured such that it defines, on the one hand, a channel together with the carrier plate and, on the other hand, a capacitive pressure sensor together with the carrier plate. The channel is implemented such that it defines a flow resistance. The capacitive pressure sensor is defined by a membrane and an associated membrane electrode as well as by a counterelectrode arranged on the carrier plate in spaced relationship with said membrane electrode. According to U.S. Pat. No. 5,377,524, the capacitive pressure sensor is arranged outside of the flow path, viz. in a lateral branch, so as to permit the measurement of a pressure difference between the pressure prevailing at the inlet opening and the pressure prevailing at the outlet openig.
In Boillat, M. A. et al: "A Differential Pressure Liquid Flow Sensor for Flow Regulation and Dosing Systems", PROC. IEEE MICRO ELECTROC MECHANICAL SYSTEMS 1995, 29.1.95-2.2.95, NL-Amsterdam, pp. 350-352, a flow sensor is described in the case of which two piezoresistive low-pressure sensors are provided for detecting the pressure in the flow path in front of and behind a channel constituting a flow-restriction.